Turns out, people with vaginas also respond to their sleep cycle, and they can have increased clitoral and vaginal engorgement during the REM stage of sleep, says Aleece Fosnight, MSPAS, PA-C, a urology physician assistant and a sexual health counselor. "The clitoris has erectile tissue just like the penis, but instead of being out in the open for everyone to see, the clitoral engorgement happens internally and most women aren't aware of the process," Fosnight says.

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Here's how it works: During REM sleep, your body pumps oxygen-rich blood to your genital tissues to keep your genitals healthy, Fosnight says. This is also what happens when a person with a vagina gets aroused by something sexual: The erectile tissue in the clitoris becomes engorged and red because of the changes in circulation and heart rate, says Shannon Chavez, PsyD, a certified clinical sexologist. "The labia also has erectile tissue, and can become larger and more red in colour as the arousal triggers a release of blood flow through the entire genital area," she says. A person's vagina could also get wetter or more lubricated during these bouts of arousal.

But, like penises, the changes your genitals experience at night don't always occur because you're exposed to something that arouses you — they just sort of happen. (Though if you woke up during one of these periods when your body thinks it's aroused, you could subsequently feel more aroused and want to have sex, Fosnight says.)

That being said, some people do feel extra aroused in the morning, regardless of what their genitals are doing, because that's when people's testosterone levels peak, Dr. Chavez says. "This hormone is responsible for triggering feelings of sexual desire," she says. You also might feel hornier in the morning because you're more refreshed, relaxed, and comfortable than you are at night, according to Dr. Chavez. "This is the perfect formula for sexual arousal to take place," she says, since sex at night can feel like work for some people, because you're stressed and have used all your energy during the daytime. "There is lower tension in the morning when you are about to start the day ahead," Dr. Chavez says.

So there you go: Women can have it all, even "morning wood." There are tons of reasons why a person feels aroused when they do, but the time of day might have something to do with it after all. The next time you wake up with an urge to have sex, do it — morning sex is awesome, and your body knows it.